diff --git a/dom/security/nsCSPContext.cpp b/dom/security/nsCSPContext.cpp
index 13d6233bbaee..4d403587fcaf 100644
--- a/dom/security/nsCSPContext.cpp
+++ b/dom/security/nsCSPContext.cpp
@@ -314,17 +314,27 @@ nsresult nsCSPContext::InitFromOther(nsCSPContext* aOtherContext) {
 
   mSkipAllowInlineStyleCheck = aOtherContext->mSkipAllowInlineStyleCheck;
 
+  // This policy was already parsed somewhere else, don't emit parsing errors.
+  mSuppressParserLogMessages = true;
   for (auto policy : aOtherContext->mPolicies) {
     nsAutoString policyStr;
     policy->toString(policyStr);
     AppendPolicy(policyStr, policy->getReportOnlyFlag(),
                  policy->getDeliveredViaMetaTagFlag());
   }
+
+  mSuppressParserLogMessages = aOtherContext->mSuppressParserLogMessages;
+
   mIPCPolicies = aOtherContext->mIPCPolicies.Clone();
   return NS_OK;
 }
 
 void nsCSPContext::EnsureIPCPoliciesRead() {
+  // Most likely the parser errors already happened before serializing
+  // the policy for IPC.
+  bool previous = mSuppressParserLogMessages;
+  mSuppressParserLogMessages = true;
+
   if (mIPCPolicies.Length() > 0) {
     nsresult rv;
     for (auto& policy : mIPCPolicies) {
@@ -334,6 +344,8 @@ void nsCSPContext::EnsureIPCPoliciesRead() {
     }
     mIPCPolicies.Clear();
   }
+
+  mSuppressParserLogMessages = previous;
 }
 
 NS_IMETHODIMP
@@ -435,7 +447,8 @@ nsCSPContext::AppendPolicy(const nsAString& aPolicyString, bool aReportOnly,
   }
 
   nsCSPPolicy* policy = nsCSPParser::parseContentSecurityPolicy(
-      aPolicyString, mSelfURI, aReportOnly, this, aDeliveredViaMetaTag);
+      aPolicyString, mSelfURI, aReportOnly, this, aDeliveredViaMetaTag,
+      mSuppressParserLogMessages);
   if (policy) {
     if (policy->hasDirective(
             nsIContentSecurityPolicy::UPGRADE_IF_INSECURE_DIRECTIVE)) {
diff --git a/dom/security/nsCSPContext.h b/dom/security/nsCSPContext.h
index f9a5580b4cd4..85d286f90165 100644
--- a/dom/security/nsCSPContext.h
+++ b/dom/security/nsCSPContext.h
@@ -58,6 +58,10 @@ class nsCSPContext : public nsIContentSecurityPolicy {
   // Init a CSP from a different CSP
   nsresult InitFromOther(nsCSPContext* otherContext);
 
+  // Used to suppress errors and warnings produced by the parser.
+  // Use this when doing an one-off parsing of the CSP.
+  void SuppressParserLogMessages() { mSuppressParserLogMessages = true; }
+
   /**
    * SetRequestContextWithDocument() needs to be called before the
    * innerWindowID is initialized on the document. Use this function
@@ -182,6 +186,8 @@ class nsCSPContext : public nsIContentSecurityPolicy {
   nsWeakPtr mLoadingContext;
   nsCOMPtr<nsIPrincipal> mLoadingPrincipal;
 
+  bool mSuppressParserLogMessages = false;
+
   // helper members used to queue up web console messages till
   // the windowID becomes available. see flushConsoleMessages()
   nsTArray<ConsoleMsgQueueElem> mConsoleMsgQueue;
diff --git a/dom/security/nsCSPParser.cpp b/dom/security/nsCSPParser.cpp
index 6eabc471ac52..8fa1bca6d60f 100644
--- a/dom/security/nsCSPParser.cpp
+++ b/dom/security/nsCSPParser.cpp
@@ -40,7 +40,8 @@ static const uint32_t kHashSourceValidFnsLen = 3;
 /* ===== nsCSPParser ==================== */
 
 nsCSPParser::nsCSPParser(policyTokens& aTokens, nsIURI* aSelfURI,
-                         nsCSPContext* aCSPContext, bool aDeliveredViaMetaTag)
+                         nsCSPContext* aCSPContext, bool aDeliveredViaMetaTag,
+                         bool aSuppressLogMessages)
     : mCurChar(nullptr),
       mEndChar(nullptr),
       mHasHashOrNonce(false),
@@ -57,7 +58,8 @@ nsCSPParser::nsCSPParser(policyTokens& aTokens, nsIURI* aSelfURI,
       mSelfURI(aSelfURI),
       mPolicy(nullptr),
       mCSPContext(aCSPContext),
-      mDeliveredViaMetaTag(aDeliveredViaMetaTag) {
+      mDeliveredViaMetaTag(aDeliveredViaMetaTag),
+      mSuppressLogMessages(aSuppressLogMessages) {
   CSPPARSERLOG(("nsCSPParser::nsCSPParser"));
 }
 
@@ -161,6 +163,11 @@ void nsCSPParser::logWarningErrorToConsole(uint32_t aSeverityFlag,
                                            const char* aProperty,
                                            const nsTArray<nsString>& aParams) {
   CSPPARSERLOG(("nsCSPParser::logWarningErrorToConsole: %s", aProperty));
+
+  if (mSuppressLogMessages) {
+    return;
+  }
+
   // send console messages off to the context and let the context
   // deal with it (potentially messages need to be queued up)
   mCSPContext->logToConsole(aProperty, aParams,
@@ -1221,7 +1228,8 @@ nsCSPPolicy* nsCSPParser::policy() {
 
 nsCSPPolicy* nsCSPParser::parseContentSecurityPolicy(
     const nsAString& aPolicyString, nsIURI* aSelfURI, bool aReportOnly,
-    nsCSPContext* aCSPContext, bool aDeliveredViaMetaTag) {
+    nsCSPContext* aCSPContext, bool aDeliveredViaMetaTag,
+    bool aSuppressLogMessages) {
   if (CSPPARSERLOGENABLED()) {
     CSPPARSERLOG(("nsCSPParser::parseContentSecurityPolicy, policy: %s",
                   NS_ConvertUTF16toUTF8(aPolicyString).get()));
@@ -1244,7 +1252,8 @@ nsCSPPolicy* nsCSPParser::parseContentSecurityPolicy(
   nsTArray<CopyableTArray<nsString> > tokens;
   PolicyTokenizer::tokenizePolicy(aPolicyString, tokens);
 
-  nsCSPParser parser(tokens, aSelfURI, aCSPContext, aDeliveredViaMetaTag);
+  nsCSPParser parser(tokens, aSelfURI, aCSPContext, aDeliveredViaMetaTag,
+                     aSuppressLogMessages);
 
   // Start the parser to generate a new CSPPolicy using the generated tokens.
   nsCSPPolicy* policy = parser.policy();
diff --git a/dom/security/nsCSPParser.h b/dom/security/nsCSPParser.h
index a3b08e9352e2..21679d86a051 100644
--- a/dom/security/nsCSPParser.h
+++ b/dom/security/nsCSPParser.h
@@ -53,11 +53,13 @@ class nsCSPParser {
                                                  nsIURI* aSelfURI,
                                                  bool aReportOnly,
                                                  nsCSPContext* aCSPContext,
-                                                 bool aDeliveredViaMetaTag);
+                                                 bool aDeliveredViaMetaTag,
+                                                 bool aSuppressLogMessages);
 
  private:
   nsCSPParser(policyTokens& aTokens, nsIURI* aSelfURI,
-              nsCSPContext* aCSPContext, bool aDeliveredViaMetaTag);
+              nsCSPContext* aCSPContext, bool aDeliveredViaMetaTag,
+              bool aSuppressLogMessages);
 
   ~nsCSPParser();
 
@@ -209,6 +211,7 @@ class nsCSPParser {
   nsCSPPolicy* mPolicy;
   nsCSPContext* mCSPContext;  // used for console logging
   bool mDeliveredViaMetaTag;
+  bool mSuppressLogMessages;
 };
 
 #endif /* nsCSPParser_h___ */
diff --git a/dom/security/nsContentSecurityUtils.cpp b/dom/security/nsContentSecurityUtils.cpp
index 8e4beeb3b420..5375358b2e2a 100644
--- a/dom/security/nsContentSecurityUtils.cpp
+++ b/dom/security/nsContentSecurityUtils.cpp
@@ -1005,6 +1005,11 @@ nsresult CheckCSPFrameAncestorPolicy(nsIChannel* aChannel,
   }
 
   RefPtr<nsCSPContext> csp = new nsCSPContext();
+  // This CSPContext is only used for checking frame-ancestors, we
+  // will parse the CSP again anyway. (Unless this blocks the load, but
+  // parser warnings aren't really important in that case)
+  csp->SuppressParserLogMessages();
+
   nsCOMPtr<nsIURI> selfURI;
   nsAutoString referrerSpec;
   if (httpChannel) {
diff --git a/parser/html/nsHtml5TreeOpExecutor.cpp b/parser/html/nsHtml5TreeOpExecutor.cpp
index 17d2c7d96c19..da570e5b6dba 100644
--- a/parser/html/nsHtml5TreeOpExecutor.cpp
+++ b/parser/html/nsHtml5TreeOpExecutor.cpp
@@ -1374,7 +1374,9 @@ void nsHtml5TreeOpExecutor::AddSpeculationCSP(const nsAString& aCSP) {
   nsresult rv = NS_OK;
   nsCOMPtr<nsIContentSecurityPolicy> preloadCsp = mDocument->GetPreloadCsp();
   if (!preloadCsp) {
-    preloadCsp = new nsCSPContext();
+    RefPtr<nsCSPContext> csp = new nsCSPContext();
+    csp->SuppressParserLogMessages();
+    preloadCsp = csp;
     rv = preloadCsp->SetRequestContextWithDocument(mDocument);
     NS_ENSURE_SUCCESS_VOID(rv);
   }